Metamorphic evolution of high-pressure and ultrahigh-temperature granulites from the Highland Complex, Sri Lanka Yasuhito Osanai a, * , Krishnan Sajeev b , Masaaki Owada c , K.V.Wilbert Kehelpannala d , W.K.Bernard Prame e , Nobuhiko Nakano a , Sarath Jayatileke f a Division of Evolution of Earth Environments, Graduate School of Social, Cultural Studies, Kyushu University, Fukuoka 810-8560, Japan b Research Institute of Natural Sciences, Okayama University of Science, Okayama 700-0005, Japan c Department of Earth Science, Yamaguchi University, Yamaguchi 753-8512, Japan d Institute of Fundamental Studies, Hantana Road, Kandy, Sri Lanka e Geological Survey and Mines Bureau, Dehiwala, Sri Lanka f Industrial Technology Institute, Colombo 7, Sri Lanka Received 16 December 2003; received in revised form 24 May 2004; accepted 24 September 2004 Abstract SapphirineCquartz-bearing pelitic granulites, garnet–clinopyroxene–quartz-bearing mafic granulites and quartzo-feldspathic granulites with corundum–garnet–quartz constitute rare but important members of the Highland Complex in Sri Lanka. Peak metamorphic conditions from the Highland Complex generally have been considered to be up to w850–900 8C and w8 10 kbar. However, this study on the above mentioned rocks indicates that ultrahigh-temperature and high-pressure conditions (O1100 8C and w12 kbar) were attained during peak conditions. A metamorphic evolution of the ultrahigh-temperature metamorphic rocks was determined from careful analyses of shifts in divariant assemblages and reaction textures. This shows a clockwise P–T path from more high-pressure conditions (w1000 8C and w17 kbar; stage 0 as part of the prograde metamorphic path) to lower-pressure and -temperature conditions (w950 8C and w9 kbar; stage 4 as part of the retrograde path) through the peak metamorphic conditions (stage 1). Widespread lower pressure and temperature granulite-facies metamorphic rocks surround the ultrahigh-temperature granulites and are interpreted to have formed by the strong effect of the retrograde metamorphism and deformation. The widely reported Pan-African metamorphic ages derived from similar granulite-facies metamorphic rocks in the Gondwana fragments (Highland Complex in Sri Lanka, Lu ¨tzow-Holm Complex in east Antarctica, etc.) may also be the result of retrograde metamorphism of ultrahigh- temperature metamorphic rocks. There remains a possibility that this early ultrahigh-temperature/high-pressure granulite-facies metamorphism in the Highland Complex, as well as that in the Lu ¨tzow-Holm Complex, might pre-date Pan-African metamorphism. q 2006 Elsevier Ltd. All rights reserved. Keywords: High-pressure mafic granulite; UHT-pelitic granulites; Clockwise P–T path; Highland Complex; Sri Lanka 1. Introduction The Sri Lankan metamorphic basement has been subdivided into three major units, namely, the Vijayan Complex in the east, the Highland Complex in the central and the Wanni Complex in the west (Kehelpannala, 1997; Fig. 1). The basis for this new subdivision is Nd-model age determinations covering the entire basement (Milisenda et al., 1988; Kro ¨ner et al., 1991; Liew et al., 1991). The Vijayan Complex consists mainly of amphibolite-facies granitoid rocks, metadiorites, metagabbros and migmatites (e.g. Cooray, 1984; Kro ¨ner et al., 2003; Kehelpannala, 2004), while the Highland Complex is composed of pelitic, mafic and quartzo-feldspathic granulites, abundant charnockitic rocks, marble and quartzite, all metamorphosed to granulite-facies conditions. Some of these granulites contain ultrahigh-temperature assemblages. Rocks in the Wanni Complex are metapelites, metasemipelites, quartzites, charnockites, metagabbro, metadiorite, and meta- granitoids and are metamorphosed to upper amphibolite to granulite facies conditions. Characteristic arrested charnock- ites can also be found in the Wanni Complex (e.g. Hansen et al., 1987; Hiroi et al., 1990, 1994; Ogo et al., 1992; Kehelpannala, 1999). Journal of Asian Earth Sciences 28 (2006) 20–37 www.elsevier.com/locate/jaes 1367-9120/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2004.09.013 * Corresponding author. Fax: C81 92 726 4843. E-mail address: osanai@scs.kyushu-u.ac.jp (Y. Osanai).